O.A. Aina

The dependence of the electrical and optical properties of molecular beam epitaxial In 0.52 Al 0.48 As on growth parameters: interplay of surface kinetics and thermodynamics

The optical and transport properties of In0.52Alo.48As grown by molecular beam epitaxy have been studied as a function of growth temperature in the range of 300-520° C. It is evident that under our growth conditions, thermodynamic considerations become important, and combined with surface kinetics, clustering effects become most severe for growth temperatures around 400° C. The clustering effects are manifested by changes in low-temperature photoluminescence, Hall transport and in the properties of Schottky diodes made on the films and the relevant parameters show a peaking for growth at 400° C. In particular, the Hall mobility exhibits a turning point forT > 300 K, beyond which the mobility increases with increasing temperature. In addition, the Hall electron concentration exhibits an anomalous reduction in value in the same high-temperature range. Measurements were also made on In0.52Al0.48As grown at 620-650° C by metalorganic chemical vapor deposition. While these films exhibit the same turning point in Hall mobility, the reduction in carrier concentration is significantly absent. Analysis of these data therefore indicates that the turning point in the mobility, which is present for both growth techniques, is caused by small clusters (~35Å) of phases slightly different from the mean composition. The reduction in electron concentration, seen only in the molecular beam epitaxial samples, suggest a more severe phase separation. A simple analysis for the sample grown at 400° C indicates that the compositions In0.60Al0.40As and In0.44Al0.56As might be present, in addition to the mean lattice-matched composition.

A 1.45-W/mm, 30-GHz InP-channel power HEMT

The authors report the fabrication of the first AlInAs/InP power HEMT with a saturated power density of 1.45 W/mm, a maximum power-added efficiency of 24%, and a large signal gain of 6.2 dB at 30 GHz. The authors show that the estimated power performance of this device at the highest frequencies is better than for any three-terminal devices because the f/sub t/ of the power HEMT is high, even at high drain-source bias.<<ETX>>

Photoluminescence characterization of single heterojunction quantum well structures

A photoluminescence emission band at 830 nm has been detected in single heterojunction quantum well structures (modulation‐doped structures) in the range of 250–400 K. This emission band is observed neither in heterojunction structures without a two‐dimensional electron gas (2DEG), nor in n+ AlGaAs and GaAs. The intensity of the emission band increases as the mobility of the samples with 2DEG and shows excitonic behavior in its variation with incident laser excitation intensity. This photoluminescence emission was observed in samples grown by both molecular beam epitaxy and by organometallic vapor phase epitaxy. This effect may be useful as a rough identification of high quality, modulation‐doped heterostructures.

Halogen lamp rapid thermal annealing of Si- and Be-implanted In0.53Ga0.47As

Halogen lamp rapid thermal annealing was used to activate 100 keV Si and 50 keV Be implants in In0.53Ga0.47As for doses ranging between 5 × 1012−4 × 1014 cm−2. Anneals were performed at different temperatures and time durations. Close to one hundred percent activation was obtained for the 4.1 × 1013 cm−2 Si-implant, using an 850° C/5 s anneal. Si in-diffusion was not observed for the rapid thermal annealing temperatures and times used in this study. For the 5 × 1013 cm−2 Be-implant, a maximum activation of 56% was measured. Be-implant depth profiles matched closely with gaussian profiles predicted by LSS theory for the 800° C/5 s anneals. Peak carrier concentrations of 1.7 × 1019 and 4 × 1018 cm−3 were achieved for the 4 × 1014 cm−2 Si and Be implants, respectively. For comparison, furnace anneals were also performed for all doses.

Responses of InP/Ga0.47In0.53As/InP heterojunction bipolar transistors to 1530 and 620 nm ultrafast optical pulses

An npn InP/Ga0.47In0.53As/InP heterojunction bipolar transistor with a unity‐gain frequency of 15 GHz was illuminated with ultrafast optical pulses at wavelengths of 620 and 1530 nm. The device responded to the pulses with an emitter current transient having a duration of 12 ps, corresponding to a bandwidth of ∼40 GHz. A slower photocurrent component, with a decay time of ∼100 ps, was a sensitive function of base bias and, because of the photocarrier dynamics and the grounded‐collector circuit configuration, could be nulled out.

DC and RF characterization of short-gate-length InGaAs/InAlAs MODFETs

Lattice-matched InGaAs/InAlAs MODFETs with gate lengths down to 0.15 mu m have been fabricated and characterized. A large discrepancy is found between the g/sub m/ measured at DC and microwave frequencies and is attributed to the finite time constant of electron emission from deep traps in the InAlAs. A maximum f/sub T/ of 112 GHz is measured on a 0.15- mu m gate-length device. Devices with more shallow recessed gates are found to have a 50% larger output conductance, which causes the devices to exhibit an f/sub T/ that is greater than f/sub max/. >

Highly stable microwave performance of InP/InGaAs HIGFETs

The fabrication and microwave performance of InP/InGaAs heterojunction insulated-gate FETs (HIGFETs) using plasma-enhanced chemical vapor deposition (PECVD)-deposited SiO/sub 2/ as the gate insulator are discussed. Extrinsic transconductances as high as 240 mS/mm were obtained. Although these devices had a drain current drift of 20% under DC bias, when operated at 5 GHz they exhibited negligible drain current drift. The observation of high transconductance and stable microwave performance makes these HIGFETs ideal candidates for microwave power applications. >

Undoped InP/InGaAs heterostructure insulated-gate FET's grown by OMVPE with PECVD-deposited SiO/sub 2/ as gate insulator

The fabrication and performance of InP/InGaAs insulated-gate FETs which use a heterojunction to isolate the channel electrons from the semiconductor-insulator interface are discussed. Plasma-enhanced chemical vapor deposition (PECVD) was used to deposit SiO/sub 2/ on InP to form the gate insulator. Since the device structure is undoped, channel electrons are accumulated by the gate-induced field across the insulator. Extrinsic transconductances of 130 mS/mm (300 K) and 210 mS/mm (77 K) were achieved for 1.5- mu m gate-length devices. Gate-drain breakdown voltages in excess of 20 V were also measured.<<ETX>>

DC and RF characteristics of doped multichannel AlAs/sub 0.56/Sb/sub 0.44//In/sub 0.53/Ga/sub 0.47/As field effect transistors with variable gate-lengths

Depletion-mode doped-channel field effect transistors (DCFETs) using a AlAs/sub 0.56/Sb/sub 0.44//In/sub 0.53/Ga/sub 0.47/As heterostructure with multiple channels grown by molecular beam epitaxy (MBE) on an InP substrate are presented. Devices with gate lengths ranging from 0.2 /spl mu/m to 1.0 /spl mu/m have been fabricated. Three doped In/sub 0.53/Ga/sub 0.47/As channels separated by undoped AlAs/sub 0.56/Sb/sub 0.44/ layers are used for the devices. The devices exhibit unity current gain cut-off frequencies typically between 18 GHz and 73 GHz and corresponding maximum oscillation frequencies typically between 60 GHz and 160 GHz. The multiple channel approach results in wide linearity of dc and RF performance of the device.

Charge-control modeling of InGaAs/InP heterojunction insulated-gate FETs

A new charge-control model for accumulation-mode heterojunction FETs is presented, This model is used to determine the mobile charge density of the heterojunction channel as a function of the gate voltage. It is the result of a self-consistent combination of semiclassical and quantum-mechanical models. It is shown that the two models can be combined to provide a computationally simple description of the gate control of channel conductivity, and hence gate control of the FETs I-V characteristics. This merging of two modeling approaches results in a new, easily used, and generalized model with broad applicability to undoped heterostructure devices. A figure of merit called the crossover point, which is the gate voltage at which the sheet charge density in the InP cladding layer is equal to the sheet charge in the 2DEG, is defined. This crossover voltage is found to decrease with increasing InP thickness, which leads to reduced device performance. >